CDRIVER-5877 avoid aligned_alloc on MacOS prior to 10.15

[barracuda156]

@NattyNarwhal Could you please review this? Pre-Catalina macOS need the same fix as you have added for AIX in 9fe8af1

[NattyNarwhal]

This looks correct for macOS, but it might not be correct for iOS builds (as that will be __APPLE__ but I'm unsure if MAC_OS_X_VERSION_MIN_REQUIRED is set).

That said, as mentioned in GH-1480, the right longer term fix would be putting a check in CMake/autoconf (and propagating it to things that vendor mongo-c-driver with their own build system; i.e. the PHP extension).

[eramongodb]

Created CDRIVER-5876 to track relocating aligned_alloc availability checks from preprocessor directives into the build system.

[eramongodb]

The difficulty of finding official documentation for <AvailabilityMacros.h> and its provided features makes me hesitant to depend on it. This may nevertheless suffice as a temporary solution until CDRIVER-5876 is resolved.

[eramongodb]

Suggested change

	!defined(_AIX) && !(defined(__APPLE__) & MAC_OS_X_VERSION_MIN_REQUIRED < 101500)
	!defined(_AIX) && !(defined(MAC_OS_X_VERSION_MIN_REQUIRED) && MAC_OS_X_VERSION_MIN_REQUIRED < 101500)

Use logical OR rather than bitwise OR. Additionally recommend adjusting the condition to test for the definition of MAC_OS_X_VERSION_MIN_REQUIRED instead of defined(__APPLE__) (already used to condition the inclusion of <AvailabilityMacros.h> above) to guard against the possibility of OSX_DEPLOYMENT_TARGET and/or -mmacosx-version-min interfering with the presence of the macro (not a configuration space we control nor test).

[eramongodb]

Noting here for future reference that the value of 101500 (MacOS 10.15) is consistent with libc++'s own checks for aligned_alloc support:

// It is not yet possible to use aligned_alloc() on all Apple platforms since
// 10.15 was the first version to ship an implementation of aligned_alloc().
#  if defined(__APPLE__)
#    if (defined(__ENVIRONMENT_MAC_OS_X_VERSION_MIN_REQUIRED__) &&                                                     \
         __ENVIRONMENT_MAC_OS_X_VERSION_MIN_REQUIRED__ < 101500) ||                                                    \
        /* ... */
#      define _LIBCPP_HAS_C11_ALIGNED_ALLOC 0
#    else
#      define _LIBCPP_HAS_C11_ALIGNED_ALLOC 1
#    endif
#  elif /* ... */

[eramongodb]

Filed CDRIVER-5877 to track this PR.

[kevinAlbs]

Thank you for alerting us of this issue @barracuda156. CDRIVER-5876 applies a fix within CMake to detect if aligned_alloc is available. CDRIVER-5876 was released in 1.30.0.

[barracuda156]

@kevinAlbs Thank you very much, great! (Sorry for a delayed reply, a lot of stuff in the pipeline.)

[kevinAlbs]

@kevinAlbs Thank you very much, great! (Sorry for a delayed reply, a lot of stuff in the pipeline.)

Hah no worries. And thanks to @eramongodb for the change. I only reviewed it :)